SearcherTaxonomyManager.acquire() spins forever at 100% CPU, instead of throwing the LUCENE-5436 IllegalStateException, when the current pair's taxonomy reader was closed outside the manager

Finding LFV-250Area: facet / taxonomy (SearcherTaxonomyManager.getRefCount and tryIncRef; the misuse guard in core ReferenceManager.acquire)Priority: lowImpact: hangNovelty: known upstream

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You use SearcherTaxonomyManager and, through a bug in your own code, call decRef() or close() on the taxonomy reader of a pair you acquired (for example by wrapping pair.taxonomyReader() in try-with-resources), then release the pair as usual. Since LUCENE-5436 (4.7.0) the next acquire() is meant to detect such an outside reference-count change and throw IllegalStateException, which is what SearcherManager and the index-reader half of the same pair do. Instead acquire() retries forever in a busy loop, because SearcherTaxonomyManager.getRefCount reports only the index reader's count, so the guard never sees that the taxonomy reader is closed; only closing the manager ends the loop, with AlreadyClosedException.

Expected vs actual

Expected: The test passes: it asserts the documented behaviour.
Actual: acquire() retries forever in a busy loop, because SearcherTaxonomyManager.getRefCount reports only the index reader's count, so the guard never sees that the taxonomy reader is closed; only closing the manager ends the loop, with AlreadyClosedException.

Files

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
Tested on Lucene main ea57360912ed (2026-10-24): reproduced.
How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:$LUCENE/lucene/facet/build/libs/lucene-facet-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes-src -cp "$CP" $(find src -name '*.java')
javac -d classes-src2 -cp "$CP" $(find src2 -name '*.java')

# run 1: assertions on, seed DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes-src:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.facet.taxonomy.TestSearcherTaxonomyManagerIllegalDecRef
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes-src2:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.facet.taxonomy.TestSearcherTaxonomyManagerIllegalDecRef

The module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Formal models and scripts this finding's part of the hunt used: nrt-reference-managers

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.